1. Field of the Invention
The present invention relates to a drive device, a lens barrel, and an imaging apparatus.
2. Description of the Related Art
In imaging apparatuses such as digital cameras, video cameras, and the like, there has been proposed the following position control in order to accurately drive an optical element such as a lens. In other words, an imaging apparatus rotates a pulse plate such as a screw, a propeller, or the like by mainly using a stepping motor or the like and detects a count of the pulse plate using a detecting unit such as a photo interrupter to thereby perform position control.
Japanese Patent Laid-Open No. 2000-193877 discloses a camera that includes a screw portion extending from a drive unit in the optical axis direction and a shaft portion extending coaxial with the axis of the screw portion and rotatably supports the screw portion by receiving both ends of the screw portion with a bearing. When the screw portion rotates by the driving of the drive unit, a driven unit screwed to the screw portion travels along the straight line together with a feed female screw. A pulse plate such as a propeller is attached to the distal end of the shaft portion. With this arrangement, the camera detects the movement of the pulse plate using a detecting unit such as a photo interrupter and performs position control of the driven unit with high accuracy by controlling the rotation of the screw portion.
FIG. 12 is a diagram illustrating an example of a configuration of a lens barrel provided in the camera disclosed in Japanese Patent Laid-Open No. 2000-193877 and a drive device within the lens barrel. In the camera disclosed in Japanese Patent Laid-Open No. 2000-193877, a pulse plate 121 that controls the rotation of a screw is attached to the distal end of a shaft portion so as to be retrofittable in consideration of easiness of assembly. However, in the configuration, a flexible substrate that connects photo interrupters for detecting the movement of the pulse plate 121 is extended because the pulse plate 121 is attached to the distal end of the shaft portion, resulting in an increase in costs. In addition, since the pulse plate 121 is attached to the distal end of the shaft portion in the camera, other components must be structured so as to avoid the pulse plate 121, resulting in a reduction in the degree of freedom in design. Furthermore, since the distance between the drive unit and the pulse plate 121 is long in the camera, the vibration of the pulse plate increases, resulting in an adverse effect on controllability.